1. Technical Field
The present disclosure relates generally to the field of universal joints and more particularly to universal joints used in down hole mud motors.
2. Background Art
Down hole mud motors are used within the oil industry for earth boring operations. These mud motors rotate eccentrically. The eccentric rotation must be converted into concentric rotation in order for the drill bit to function correctly. The current state of the art generally accomplishes this conversion by providing a drive shaft having some type of universal joint connection that connects the down hole motor to a drive assembly rotating the drill bit.
U.S. Pat. No. 7,004,843 discloses a universal joint assembly including a pair of interfacing joint member assemblies that are loosely retained one to the other by a connecting rod. This arrangement allows torque to be transmitted from one member to the other via interfacing jaw portions while still allowing for angular defection. The joint member assemblies further include retainer pins and setscrews. The interfacing ends of the joint members are machined in a manner whereby the ends of each cylinder are centrally bored creating a tapered blind bore. Each cylinder is then diametrically quartered outwardly from the central axis with opposing quarters removed for a predetermined depth, thus leaving a pair of wedge shaped, opposing mortised tangs. The tangs are slightly smaller in width than the removed quarter portions, thus allowing for a loose fit when interfacing the two joint members. A hardened steel cylindrical bearing member is slidably located in the bottom of the blind hole in each of the cylindrical joint body members. The connecting rod has a reduced diametrical neck portion and a radial or crowned head portion at each end. At assembly a portion of the connecting rod is slidably inserted into the blind bores of each of the body members. The connecting rod has sufficient length so as to maintain spacing between the body members relative to the connecting rod.
In the assemblies disclosed in the '843 patent, the body members are each bored perpendicularly to accept two parallel retaining pins at points intersecting the respective neck portions of the connecting rod. Sufficient clearance between the neck portions of the connecting rod and the parallel retaining pins is provided to allow the connecting rod to slide, rotate within the body members and make pivotal contact with the bearing members. The parallel bores extend clear through the joint members, thereby allowing access to the retaining pins for removal. The bores are then counter bored to receive the retaining pins and counter bored again and tapped to receive setscrews.
Replacement of the joint or its components is a costly operation and thus to be avoided if at all possible. Operators and service companies continuously seek down hole components possessing higher tensile strength and/or higher overpull capacity. While the assemblies disclosed in the '843 patent are admirable, assemblies having even higher tensile strength and/or higher overpull capacity are desired, as are components possessing greater performance and life expectancy.